GRAPHENE PAINT

Field of Invention

This invention relates to a graphene formulation for use in protective paint coatings.

Background

The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

In the oil and gas industry, corrosion is the main factor that contributes to the ageing and failures of metallic structures. Polymeric protective coating is a common technology used to protect the metal components from corrosion. As for critical areas such as a splash zone, the epoxy glass flake paint (GF) is a typical grade of coating used to protect the structure which includes jacket legs, risers, and platform decks. However, due to consistent and long exposure of the coating under harsh environment such as saltwater and ultraviolet (UV) light, the coating may degrade and lose the contact adhesion between the coating and metal substrate.

Recent studies have highlighted the unique properties of single atom thick sheet of graphene, and this material has been extensively used to improve mechanical, chemical, electrical and barrier properties of polymers. As a barrier application, the tortuous pathway created in the polymer coating layer from the thin layer structure of graphene could restrict gas and even small water molecules from penetrating the coated metal substrate (B. Tan & N. L. Thomas, J. Membr. Sci. 2016, 514, 595-612). Apart from that, the dense lattice structure of the graphene prevents any material, including the smallest atom of helium, from penetrating it. The performance of graphene material has been reported to be highly dependent on their thickness, aspect ratio and surface area (B. Tan & N. L. Thomas, J. Membr. Sci. 2016, 514, 595-612; and C. H. Chang et al., Carbon 2012, 50, 5044-5051). However, most of the graphene studies focused only on neat epoxy which is not fully formulated paint, and contains pigment, filler and other additives.

Therefore, there is a need to discover new and fully formulated graphene-based paint formulations with enhanced resistance, mechanical, chemical, and electrical properties, and durability. Summary of Invention

The inventors have surprisingly found that the problems discussed above may be solved by an additive based on graphene. The disclosed graphene-based paint not only has improved water barrier and mechanical properties, but it also has enhanced corrosion resistance and minimised paint degradation. Advantageously, the graphene-based additive can extend the service life of the graphene-based paint coating.

In a first aspect of the invention, there is provided a resin-based formulation comprising: a resin material; a filler material; and graphene flakes.

In embodiments of the first aspect of invention:

(a) the resin material may be a thermoset material (e.g. selected from one or more of an acrylic resin, a polyester resin, an epoxy resin, a polyurethane resin, an alkyd resin, a phenolic resin, a urea resin, a fluororesin, a polyester-urethane resin, an epoxy-polyester resin, an acrylic-polyester-based resin, an acrylic-urethane resins, an acrylic-melamine resins, and a polyester-melamine resin, optionally wherein the thermosetting resin is selected from one or more of an acrylic resin, a polyester resin, an epoxy resin, a polyurethane resin, a polyester resin, and an alkyd resin);

(b) the resin material may be a thermoplastic material (e.g. selected from one or more of a polyethylene resin, a polypropylene resin, a petroleum resin, a thermoplastic polyester, and a thermoplastic fluororesin);

(c) the total amount of graphene flakes may be from 0.02 to 2 wt% relative to the total weight of the resin material and the filler material; and

(d) the filler material may be selected from one or more of the group selected from glass flakes, calcium carbonate, talc, clay, barium sulphate, zinc, and zinc silicate optionally wherein the filler material is glass flakes.

In a second aspect of the invention, there is provided a paint formulation comprising: a resin material; a filler material; graphene flakes; and a curing agent.

In embodiments of the second aspect of invention: (a) the resin material may be a thermoset material (e.g. selected from one or more of an acrylic resin, a polyester resin, an epoxy resin, a polyurethane resin, an alkyd resin, a phenolic resin, a urea resin, a fluororesin, a polyester-urethane resin, an epoxy-polyester resin, an acrylic-polyester-based resin, an acrylic-urethane resins, an acrylic-melamine resins, and a polyester-melamine resin, optionally wherein the thermosetting resin is selected from one or more of an acrylic resin, a polyester resin, an epoxy resin, a polyurethane resin, a polyester resin, and an alkyd resin);

(b) the resin material may be a thermoplastic material (e.g. selected from one or more of a polyethylene resin, a polypropylene resin, a petroleum resin, a thermoplastic polyester, and a thermoplastic fluororesin);

(c) the total amount of graphene flakes may be from 0.04 to 3 wt% relative to the total weight of the resin material, the curing agent and the filler material;

(d) the filler material may be selected from one or more of the group selected from glass flakes, calcium carbonate, talc, clay and barium sulphate, optionally wherein the filler material is glass flakes; and

(e) the curing agent may be selected from one or more of the group selected from a polyisocyanate, an amine, a polyamide, a polybasic acid, an acid anhydride, a polysulfide, a trifluoroboric acid, an acid dihydrazide, and an imidazole.

In a third aspect of the invention, there is provided a kit of parts formed from a resin-based formulation as defined in the first aspect of the invention, and a curing agent (e.g. selected from one or more of the group selected from a polyisocyanate, an amine, a polyamide, a polybasic acid, an acid anhydride, a polysulfide, a trifluoroboric acid, an acid dihydrazide, and an imidazole), and any technically sensible combination of its embodiments.

Further aspects and embodiments of the invention are described in the following clauses.

1 . A resin-based formulation, comprising: a resin material; a filler material; and graphene flakes, wherein the total amount of graphene flakes is from 0.02 to 2 wt% relative to the total weight of the resin material and the filler material.

2. The resin-based formulation according to Clause 1 , wherein the graphene flakes have a thickness of from 1 to 15 nm, such as from 1.5 to 10 nm, such as from 2 to 7 nm, such as from 3 to 5 nm. 3. The resin-based formulation according to Clause 1 or Clause 2, wherein the resin is a thermosetting resin or a thermoplastic resin.

4. The resin-based formulation according to Clause 3, wherein the thermosetting resin is selected from one or more of an acrylic resin, a polyester resin, an epoxy resin, a polyurethane resin, an alkyd resin, a phenolic resin, a urea resin, a fluororesin, a polyester-urethane resin, an epoxy- polyester resin, an acrylic-polyester-based resin, an acrylic-urethane resins, an acrylic-melamine resins, and a polyester-melamine resin, optionally wherein the thermosetting resin is selected from one or more of an acrylic resin, a polyester resin, an epoxy resin, a polyurethane resin, a polyester resin, and an alkyd resin.

5. The resin-based formulation according to Clause 3, wherein the thermoplastic resin is selected from one or more of a polyethylene resin, a polypropylene resin, a petroleum resin, a thermoplastic polyester, and a thermoplastic fluororesin.

6. The resin-based formulation according to any one of the preceding clauses, wherein the formulation further comprises a curing agent, optionally wherein the curing agent is selected from one or more of the group selected from a polyisocyanate, an amine, a polyamide, a polybasic acid, an acid anhydride, a polysulfide, a trifluoroboric acid, an acid dihydrazide, and an imidazole.

7. The resin-based formulation according to any one of the preceding clauses, wherein the wt:wt ratio of the resin material to the glass flakes is from 60:40 to 90:10, such as from 70:30 to 85:15, such as 80:20.

8. The resin-based formulation according to any one of the preceding clauses, wherein the total amount of graphene flakes is from 0.03 to 1 .5 wt%, such as from 0.05 to 1 wt%, such as from 0.07 to 0.5 wt%, such as from 0.0625 to 0.25 wt% relative to the total weight of the resin material and the filler material.

9. The resin-based formulation according to any one of the preceding clauses, wherein the filler material is selected from one or more of the group selected from glass flakes, calcium carbonate, talc, clay, barium sulphate, zinc, and zinc silicate optionally wherein the filler material is glass flakes. 10. The resin-based formulation according to any one of the preceding clauses, wherein the formulation further comprises one or more additives selected from the list:

(a) a colour pigment, optionally wherein the colour pigment is selected from one or more of the group consisting of titanium oxide, silica, mica, calcium carbonate, zinc oxide, and clays;

(b) a silicone;

(c) a rheology modifier;

(d) a fungicide and/or an algaecide;

(e) a dispersant;

(f) a surfactant;

(g) an additive that prevents a paint from drying too quickly;

(h) a preservative; and

(i) a UV absorber.

11 . The resin-based formulation according to any one of the preceding clauses, wherein the formulation further comprises a solvent, optionally wherein the solvent is selected from one or more of the group consisting of white spirits, acetone, turpentine, naphta, toluene, methyl ethyl ketone (MEK), dimethylformamide (DMF), glycol ethers, ethylbenzene, xylene, n- butylacetate, butanol, and water.

12. A paint formulation, comprising: a resin material; a filler material; graphene flakes; and a curing agent, wherein the total amount of graphene flakes is from 0.04 to 3 wt% relative to the total weight of the resin material, the curing agent and the filler material.

13. The paint formulation according to Clause 12, wherein the graphene flakes have a thickness of from 1 to 15 nm, such as from 1 .5 to 10 nm, such as from 2 to 7 nm, such as from 3 to 5 nm.

14. The paint formulation according to Clause 12 or Clause 13, wherein the resin is a thermosetting resin or a thermoplastic resin.

15. The paint formulation according to Clause 14, wherein the thermosetting resin is selected from one or more of an acrylic resin, a polyester resin, an epoxy resin, a polyurethane resin, an alkyd resin, a phenolic resin, a urea resin, a fluororesin, a polyester-urethane resin, an epoxy- polyester resin, an acrylic-polyester-based resin, an acrylic-urethane resins, an acrylic-melamine resins, and a polyester-melamine resin, optionally wherein the thermosetting resin is selected from one or more of an acrylic resin, a polyester resin, an epoxy resin, a polyurethane resin, a polyester resin, and an alkyd resin.

16. The paint formulation according to Clause 14, wherein the thermoplastic resin is selected from one or more of a polyethylene resin, a polypropylene resin, a petroleum resin, a thermoplastic polyester, and a thermoplastic fluororesin.

17. The paint formulation according to any one of Clauses 12 to 16, wherein the formulation further comprises a curing agent, optionally wherein the curing agent is selected from one or more of the group selected from a polyisocyanate, an amine, a polyamide, a polybasic acid, an acid anhydride, a polysulfide, a trifluoroboric acid, an acid dihydrazide, and an imidazole.

18. The paint formulation according to any one of Clauses 12 to 17, wherein the wt:wt ratio of the resin material to the glass flakes is from 60:40 to 90:10, such as from 70:30 to 85:15, such as 80:20.

19. The paint formulation according to any one of Clauses 12 to 18, wherein the total amount of graphene flakes is from 0.04 to 2.5 wt%, such as from 0.045 to 2 wt%, such as from 0.05 to 1.5 wt%, such as from 0.06 to 1 wt% relative to the total weight of the resin material the curing agent and the filler material.

20. The paint formulation according to any one of Clauses 12 to 19, wherein a cured paint formulation, formed from said paint formulation, on a metal substrate provides one or more of the following:

(a) an electrical impedance resistance in the order of from 1 .0x10 ⁶ to 1 .0x10 ⁸ Ohms such as in the order of 1 .0x10 ⁷ Ohms;

(b) an adhesion strength of from 1 ,500 to 2,600 psi, such as from 2,000 to 2,500 psi, such as 2,400 psi after curing has completed;

(c) an adhesion strength of from 1 ,500 to 1 ,800 psi, such as 1 ,600 psi after a 3,000 hour salt spray test;

(d) a mass loss of less than 10 mg following an abrasion resistance test;

(e) a corrosion creepage of less than 1 .5 mm after a 3,000 hour salt spray test;

(f) no blistering after a 3,000 hour salt spray test; and

(g) no blistering after a 4,200 hour UV/salt spray test. 21 . The paint formulation according to any one of Clauses 12 to 19, wherein the filler material is selected from one or more of the group selected from glass flakes, calcium carbonate, talc, clay and barium sulphate, optionally wherein the filler material is glass flakes.

22. The paint formulation according to any one of Clauses 12 to 19, wherein the paint formulation further comprises one or more additives selected from the list:

(a) a colour pigment, optionally wherein the colour pigment is selected from one or more of the group consisting of titanium oxide, silica, mica, calcium carbonate, zinc oxide, and clays;

(b) a silicone;

(c) a rheology modifier;

(d) a fungicide and/or an algaecide;

(e) a dispersant;

(f) a surfactant;

(g) an additive that prevents a paint from drying too quickly;

(h) a preservative; and

(i) a UV absorber.

23. The paint formulation according to any one of Clauses 12 to 19, wherein the paint formulation further comprises a solvent, optionally wherein the solvent is selected from one or more of the group consisting of white spirits, xylene and water.

24. A dried paint formulation applied to a surface in need thereof, where the paint formulation is a paint formulation according to any one of Clauses 12 to 23, wherein the dried paint formulation has a dry film thickness of from 50 to 1 ,000 pm.

25. A kit of parts, comprising:

(a) resin-based formulation according to any one of Clauses 1 to 5, and 7 to 11 ; and

(b) a curing agent, optionally wherein the curing agent is selected from one or more of the group selected from a polyisocyanate, an amine, a polyamide, a polybasic acid, an acid anhydride, a polysulfide, a trifluoroboric acid, an acid dihydrazide, and an imidazole.

Drawings

FIG. 1 depicts a general overview of the graphene paint preparation stage. FIG. 2 depicts (a) appearance of graphene solution/masterbatch after sonication process; (b) dispersing homogenizing blade stirrer; and (c) the appearance of graphene mixing in epoxy GF paint.

FIG. 3 depicts the electrical impedance test setup, (a) Schematic diagram of the electrical impedance spectroscopy (EIS) cell; (b) equivalent circuit for the EIS cell; and (c) a photograph of the setup.

FIG. 4 depicts the EIS results of (a) unmodified epoxy GF paint; (b) 0.01 wt% graphene- modified epoxy GF paint; (c) 0.05 wt% graphene-modified epoxy GF paint; and (d) unmodified and 0.05 wt% graphene-modified epoxy GF paint.

FIG. 5 depicts EIS results of unmodified and 0.05 wt% graphene-modified epoxy GF paint after 168 h.

FIG. 6 depicts (a) a photograph of the abraser; (b) abrasion performance of the various paint coatings at different loading of graphene; and (c) photographs of the samples after abrasion test: (i) neat; and (ii) 0.05% graphene.

FIG. 7 depicts (a) a photograph of the samples arranged in the salt spray chamber; (b) appearance of the coated surface after 3000 h of salt spray exposure on (i) unmodified epoxy GF paint; and (ii) 0.05 wt% modified graphene proxy GF; (c) corrosion creepage size after 3000 h of salt spray exposure; and (d) scribed samples (i) before; and (ii) after salt spray exposure.

FIG. 8 depicts (a) a photograph of the pull-off adhesion test on the painted steel coupon; and (b) adhesion strength test sample.

FIG. 9 depicts adhesion strength of (a) the various paint coatings investigated; and (b) graphene-modified epoxy paint before and after 2 weeks of salt spray exposure.

FIG. 10 depicts the experimental setup for impact test.

FIG. 11 depicts photographs of the samples after impact test, (a) Neat epoxy paint; and (b) 0.05 wt% graphene. FIG. 12 depicts photographs of (a) the weathering tester; (b) samples arranged in UV chamber; and (c) UV samples holder.

FIG. 13 depicts the appearance of the graphene-modified epoxy paint surface before and after cyclic UV/salt spray test.

FIG. 14 depicts the mechanism of graphene flake as a barrier additive agent.

FIG. 15 depicts (a) cathodic disbondment of graphene-modified epoxy paint after 30 days of exposure; and (b) photograph of the sample after cathodic disbondment test.

FIG. 16 depicts the EIS results of the samples prepared from commercial epoxy GF paint.

FIG. 17 depicts the EIS comparison of commercial neat epoxy glass flake paint with graphene paint formulations at 264 h.

Description

It has been surprisingly found that the application of graphene flakes to a resin-based formulation that may be used as a paint can result in impressive gains in one or more of the electrical impedance, adhesion strength, abrasion mass loss, corrosion resistance, and blistering resistance over an extended period of time.

Thus in a first aspect of the invention, there is provided a resin-based formulation, comprising: a resin material; a filler material; and graphene flakes, wherein the total amount of graphene flakes is from 0.02 to 2 wt% relative to the total weight of the resin material and the filler material.

In embodiments herein, the word “comprising” may be interpreted as requiring the features mentioned, but not limiting the presence of other features. Alternatively, the word “comprising” may also relate to the situation where only the components/features listed are intended to be present (e.g. the word “comprising” may be replaced by the phrases “consists of’ or “consists essentially of’). It is explicitly contemplated that both the broader and narrower interpretations can be applied to all aspects and embodiments of the present invention. In other words, the word “comprising” and synonyms thereof may be replaced by the phrase “consisting of’ or the phrase “consists essentially of’ or synonyms thereof and vice versa.

In embodiments herein, various features may be described in the singular or the plural. It is herein explicitly contemplated that references to the singular are to be understood as including the plural, and references to the plural are to be understood as including the singular, unless such an interpretation would be technically illogical.

Any suitable kind of graphene flake may be used in the currently claimed invention. For example, the graphene flakes have a thickness of from 1 to 15 nm, such as from 1 .5 to 10 nm, such as from 2 to 7 nm, such as from 3 to 5 nm. Suitable graphene flakes may be commercially available and may be bought and used following dispersion as discussed in the examples section below.

As noted above, the total amount of graphene flakes in the resin-based formulation may be from 0.02 to 2 wt% relative to the total weight of the resin material and the filler material. In some embodiments of the invention, the total amount of graphene flakes in the resin-based formulation may be from 0.03 to 1.5 wt%, such as from 0.05 to 1 wt%, such as from 0.07 to 0.5 wt%, such as from 0.0625 to 0.25 wt% relative to the total weight of the resin material and the filler material.

Any suitable filler material may be used in resin-based formulation disclosed herein. Suitable filler materials include, but are not limited to glass flakes, calcium carbonate, talc, clay, barium sulphate, zinc, zinc silicate and combinations thereof. In certain embodiments that may be mentioned herein, the filler material may be glass flakes. Any suitable glass flake may be used as the filler material. For example, the glass flakes may have a maximum thickness of from 5 to 10 pm ± 2 pm and may also have a size of from 20 to 400 pm in any one direction of its planar surface.

Any suitable resin material may be used in the resin-based formulation disclosed herein. For example, the resin may be a thermosetting resin or a thermoplastic resin.

Examples of thermosetting resins that may be mentioned herein include, but are not limited to an acrylic resin, a polyester resin, an epoxy resin, a polyurethane resin, an alkyd resin, a phenolic resin, a urea resin, a fluororesin, a polyester-urethane resin, an epoxy-polyester resin, an acrylic-polyester-based resin, an acrylic-urethane resins, an acrylic-melamine resins, a polyester-melamine resin, and combinations thereof. In certain embodiments that may be mentioned herein, the thermoset material may be an acrylic resin, a polyester resin, an epoxy resin, a polyurethane resin, a polyester resin, an alkyd resin, or combinations thereof.

Examples of thermoplastic materials that may be mentioned herein include, but are not limited to a polyethylene resin, a polypropylene resin, a petroleum resin, a thermoplastic polyester, a thermoplastic fluororesin, and combinations thereof.

As will be appreciated, when there is more than one polymeric material used, the resulting polymeric matrix is a blend of the chosen polymeric materials. This may be used when particular properties are required. It is contemplated that in some embodiments, the polymeric material may be a blend comprising both thermoplastic and thermoset resins.

Thermosetting resin formulations may be used to coat critical areas of an oil rig, such as the splash zone of the rig. Thermoplastic resin formulations may be used to coat pipelines. In particular embodiments of the invention that may be mentioned herein, the resin-based formulation may use a thermosetting resin.

The resin material may be present in the resin-based formulation in any suitable amount. Suitable amounts include, but are not limited to a wt:wt ratio of the resin material to the glass flakes of from 60:40 to 90:10, such as from 70:30 to 85:15, such as 80:20.

In certain embodiments of the composition, the resin-based formulation may contain a curing agent. When used herein, “curing agent” refers to a material that may form cross-links between the polymer chains of the resin material. Any suitable curing agent may be used herein - provided that it is compatible with at least one of the resin material(s) used in the formulation. Examples of suitable curing agents that may be mentioned include, but are not limited to, a polyisocyanate, an amine, a polyamide, a polybasic acid, an acid anhydride, a polysulfide, a trifluoroboric acid, an acid dihydrazide, an imidazole, and combinations thereof.

The resin-based formulation may additionally comprise one or more additives. Any suitable additive may be used in the formulation. For example, the additive may be one of more additives selected from the list:

(a) a colour pigment (e.g. selected from titanium oxide, silica, mica, calcium carbonate, zinc oxide, and clays);

(b) a silicone;

(c) a rheology modifier;

(d) a fungicide and/or an algaecide; (e) a dispersant;

(f) a surfactant;

(g) an additive that prevents a paint from drying too quickly;

(h) a preservative; and

(i) a UV absorber.

The resin-based formulation described hereinbefore may also include a solvent in certain embodiments. The solvent may be one that is suitable for making the formulation into a paint that may be applied to a surface. Examples of suitable solvents include, but are not limited to white spirits, acetone, turpentine, naphta, toluene, methyl ethyl ketone (MEK), dimethylformamide (DMF), glycol ethers, ethylbenzene, xylene, n-butylacetate, butanol, water and combinations thereof.

As will be appreciated, afterthe formulation has been applied to a surface and has dried, there may be no solvent present or the solvent may only be present in trace quantities within the resin structure. However, any suitable amount of solvent may be present when the resin-based formulation has been prepared for use. For example, the resin-based formulation may include from 5 to 40 wt% of the total mass of the prepared formulation.

In a further aspect of the invention, there is provided a paint formulation, comprising: a resin material; a filler material; graphene flakes; and a curing agent, wherein the total amount of graphene flakes is from 0.04 to 3 wt% relative to the total weight of the resin material, the curing agent and the filler material.

For the avoidance of doubt, the paint formulation described above may have any of the features or properties described herein in relation to the composition of the resin-based formulation. As such, for brevity, materials that have been discussed in relation to the resin formulation will not be discussed again here. That is, the resin material, the filler material, the graphene flakes and the curing agent are as described hereinbefore and have the same properties. The weight to weight ratio of the resin material to the glass flakes may also be as described above for the resin-based formulation.

As noted above, the total amount of graphene flakes in the paint formulation may be from 0.04 to 3 wt% relative to the total weight of the resin material, the curing agent and the filler material. In some embodiments of the invention, the total amount of graphene flakes that may be present in the paint formulation may be from 0.04 to 2.5 wt%, such as from 0.045 to 2 wt%, such as from 0.05 to 1.5 wt%, such as from 0.06 to 1 wt% relative to the total weight of the resin material, the curing agent and the filler material.

In certain embodiments of the composition, the paint formulation may contain a solvent. Examples of solvent that may be mentioned herein include, but are not limited to white spirits, xylene and water.

The resin-based formulation may additionally comprise one or more additives. Any suitable additive may be used in the formulation. For example, the additive may be one of more additives selected from the list:

(a) a colour pigment (e.g. selected from titanium oxide, silica, mica, calcium carbonate, zinc oxide, and clays);

(b) a silicone;

(c) a rheology modifier;

(d) a fungicide and/or an algaecide;

(e) a dispersant;

(f) a surfactant;

(g) an additive that prevents a paint from drying too quickly;

(h) a preservative; and

(i) a UV absorber.

As will be appreciated, the current invention also discloses a dried paint formulation applied to a surface in need thereof, where the paint formulation is a paint formulation as described hereinbefore, wherein the dried paint formulation has a dry film thickness of from 50 to 1 ,000 pm. As will be appreciated, the dried paint formulation will be a cured paint formulation, wherein the resin has been crosslinked by the curing agent to form the film, and dispersed within the film will be the graphene flakes, the filler material and any additives so present. Additionally, the dried film may include a trace amount of the solvent used in the paint formulation, though there may be no such solvent left in the dried paint formulation.

The invention also provides a cured paint formulation, formed from the paint formulation described herein on a metal substrate, which provides one or more of the following properties: (a) an electrical impedance resistance in the order of from 1 .0x10 ⁶ to 1 .0x10 ⁸ Ohms such as in the order of 1 .0x10 ⁷ Ohms; (b) an adhesion strength of from 1 ,500 to 2,600 psi, such as from 2,000 to 2,500 psi, such as 2,400 psi after curing has completed;

(c) an adhesion strength of from 1 ,500 to 1 ,800 psi, such as 1 ,600 psi after a 3,000 hour salt spray test;

(d) a mass loss of less than 10 mg following an abrasion resistance test;

(e) a corrosion creepage of less than 1 .5 mm after a 3,000 hour salt spray test;

(f) no blistering after a 3,000 hour salt spray test; and

(g) no blistering after a 4,200 hour UV/salt spray test.

It will be appreciated that the cured (dried) paint formulation may provide all of the above properties, one of them or any combination thereof.

As will be appreciated, a fully-formed paint formulation will include the curing agent. It may be undesirable to have the curing agent in contact with the resin material until just before it is to be applied to a surface as a paint. Whether this is the case will depend on the nature of the curing agent and whether its mere contact with the resin material will start crosslinking, or if some other activation is needed (e.g. hear, air etc.). In cases where it is advisable to keep the curing agent separate, there is also provided a kit of parts, comprising:

(a) resin-based formulation as described above (excluding the curing agent); and

(b) a curing agent.

The curing agent may be selected from one or more of the group selected from a polyisocyanate, an amine, a polyamide, a polybasic acid, an acid anhydride, a polysulfide, a trifluoroboric acid, an acid dihydrazide, and an imidazole.

Further aspects and embodiments of the invention will now be described by reference to the following non-limiting examples.

Examples

Materials

The graphene material used in this project was a commercially available G1 grade graphene, with a nominal thickness of from less than 2 nm to 3, formed from 1 to 5 layers (average 3 layers) of graphene sheets having a flake thickness of from 0.3 to 1 .7 nm and a lateral size of from 400 to 550 nm. The epoxy GF paint used was a commercially available splash zone protective coating for offshore and marine applications. The glass flake concentration was approximately 20 weight percent (wt%) that constitute an overall solid content of approximately 92%. The mass ratio between the resin and curing agent was 4:1 . The metal substrates used were A36 carbon steel plates with thickness of 2.5 mm. The surfaces of the steel plates were prepared for coating as recommended for field application, viz. sand blasting to get a SA 2.5 surface profile, then cleaned with acetone before the paint was coated on the coupon using a bar coater (400 pm).

Example 1. Graphene/epoxy coating (graphene paint) preparation

The overall preparation process of the graphene paint is shown in FIG. 1.

1. The graphene concentration was calculated using 0.05 wt% or 0.1 wt% of the total paint + curing agent as a preliminary step.

2. The graphene was sonicated in a paint thinner (as specified by the paint supplier) for 1 h at a solvent to graphene ratio of 40:1 or solvent at 2 wt% of the total combination paint + curing agent. The ultrasonic bath was set at a frequency of 80 kHz, 40 °C and for 1 h. The sonication of graphene in solvent is necessary to ensure that the graphene flake can be exfoliated before it is mixed with epoxy GF paint.

3. After completing the sonication process as shown in FIG. 2a, the graphene masterbatch/solution was added into the epoxy GF paint according to the total weight of the paint.

4. The graphene solution/masterbatch should be mixed with the paint within 5 days of sonication, and if more than that, the graphene solution/masterbatch must be sonicated again for 1 h using the steps outlined in Step 2.

5. If the volume required is less than 200 mL, the graphene is mixed with the epoxy paint using an in-house blending technique through a planetary mixer. The planetary mixer is set at 1500 rpm, 0 bar, and for 5 min.

6. If the volume required exceeds 200 mL, a high-speed stirrer is employed to disperse the graphene in the epoxy GF paint. In order to achieve vortex mixing, the high-speed stirrer is set at 1000-1500 rpm, and for 30 min. The type of mixer propeller used is a “dispersing homogenizing blade” as illustrated in FIG. 2b.

7. FIG. 2c depicts the appearance of a well-mixed graphene in epoxy GF paint.

8. Once blending was completed, an amine-based curing agent was added and stirred manually for another 10 min.

9. The graphene-modified paint was finally applied on a carbon steel plate using a 400 pm thickness bar coater (RK Printcoats Instruments). The paint coatings were then allowed to cure at room temperature for a week before testing was carried out. The thickness of the cured paint coatings was measured with an Elcometer dry film thickness instrument.

Table 1. Formulation of the paint.

Example 2. Water barrier performance

EIS is a common technique that is widely used to study the electrochemical activity in order to assess the corrosion behaviour of a coated substrate. Technically, the EIS test measures electrochemical impedance, which corresponds to the ability of the coating to resist current flow. Increased impedance suggests improvement in barrier performance of the coating.

Electrical Impedance test

The barrier performance of the paint coatings was evaluated by EIS, according to ISO 16773. The electrical impedance test setup is shown in FIG. 3. A conventional three electrode cell was employed for electrochemical measurement in 3.5 wt% NaCI solution with the substrate acting as the working electrode, saturated calomel as a reference and platinum mesh as the counter electrode. The EIS cell is depicted in FIG. 3a. As shown in FIG. 3a, there is an EIS cell 100 that includes a counter electrode 110, a reference electrode 120, an electrolyte (3% NaCI) 130, and a coated panel working electrode 140. The amplitude of sinusoidal signal was 10 mV, and the frequency ranging from 102 to 105 Hz. The test was performed on specimens exposed to 3.5% NaCI for 7 days, and the results were worked out using the Bode plot, in conjunction with the Gamry software. The EIS results are presented by means of the Bode plot diagram.

Results and discussion

The water barrier performance of unmodified and modified graphene paint was investigated by observing the EIS Bode plot diagram of electrical impedance value (Ohm) at different exposure times as shown in FIG. 4a-c. It appears that the impedance value for unmodified epoxy GF paint reduced with increasing exposure in time, particularly after 48 h, suggesting electrolyte penetration into the coating film to interact with a metal substrate (X. Wang et al., Nanomaterials 2018, 8, 1005). In contrast, the impedance for the 0.01 and 0.05 wt% graphene modified paint remained stable at approximately log 10 ⁷ Q up through the tests right up to 168 h of exposure. In fact, no loss of adhesion and no blistering on the paint surface was observed. This finding indicates that the graphene particles that were well-dispersed in epoxy paint were able to form a more tortuous pathway for oxygen and water to diffuse into the layer, which could further enhance the corrosion resistance of the coating (B. Tan & N. L. Thomas, J. Membr. Sci. 2016, 514, 595-612). In addition, minimum blistering and corrosion underneath the coating is attributed to better adhesion between the metal and graphene-modified paint coatings. FIG. 5 shows a comparison in impedance value graph between unmodified epoxy GF paint and modified one at 168 h of exposure. The figure demonstrates that the graphene- modified paint system exhibited a water barrier property which is of three orders of magnitude higher than that of the unmodified paint system.

Example 3. Abrasion resistance

Abrasion resistance test

The abrasion resistance was carried out according to ASTM D4060. 1000 cycles with 1 kg of load was applied on the graphene epoxy paint surface, and the weight of the graphene epoxy paint before and after the abrasion test were measured to calculate the mass loss. The abrasion resistance of the paint coatings is related to weight loss due to continuous abrading of the surface with a standard abraser. FIG. 6a depicts a photograph of the abraser.

Results and discussion

Good abrasion resistance is desirable for a protective coating to ensure it is durable in services. FIG. 6b summarises the abrasion resistance of the neat and graphene modified paint coatings. It can be seen that the incorporation of graphene reduced the mass loss of the paint coatings, even at the lower concentration of 0.01 wt% of graphene. Even better resistance was recorded in the 0.05 wt% graphene modified paint, whereby the mass loss is only about a third of that of the neat paint coating. The abrasion of 0.05 wt% graphene modified paint was < 10 mg. This result correlates well with the recent work of Zhang et al. (M. Avella, M. E. Ericco & E. Martuscelli, Nano Lett. 2001 , 1, 213-217; and Y. Zhang et al., Coatings 2018, 8, 91) on similar graphene epoxy coatings. Their study of coefficient of friction and wear rate found gradual reduction in both properties as the loading of graphene is increased. They attributed their findings to possible self-lubrication effect of graphene, in which graphene forms stable graphene-polymer films between the contact surfaces, thus resulting in reduced friction.

Example 4. Salt spray test Salt spray test

The corrosion resistance of the paint coatings was investigated using a salt spray test in accordance with ASTM B117 and D1654. Prior to exposure, scribes (X) were deliberately created on the surface of the specimens using a pen knife of 0.5 mm blade thickness.

Specimens were placed in the salt spray chamber (FIG. 7a) at 35 °C with continuous spray of NaCI solution (5.0 wt%, pH = 6.5-7.0). Three specimens were carried out in parallel for all samples. The specimens were left in the conditioning chamber for up to 3000 h. Visual inspection of the coatings surface and creepage area were measured at the end of the test period according to ASTM 1654 to inspect for any defect present such as blister, rust, and loss of adhesion.

Results and discussion

The long-term durability of 0.05 wt% of modified graphene epoxy GF paint was selected for further long-term durability test as it gave promising result in both EIS and abrasion tests in

Examples 2 and 3, respectively. The graphene painted plate was evaluated through accelerated salt spray test by exposing the painted metal specimens with a scribed surface for 3000 h. As shown in FIG. 7b, modified graphene paint exhibited the most stable water barrier performance with less rust residue observed and corrosion underneath the coating. It can also be observed that unlike the unmodified epoxy paint, graphene-modified paint did not experience any blistering. This result concurs well with the findings observed in EIS, elucidating that the incorporation of graphene has effectively increased the barrier property and adhesion between the paint and metal substrate. In addition, the corrosion creepage area that was recorded for modified graphene paint was observed to be two times lower than that of the unmodified one, indicating a good adhesion of the coating with a metal substrate to protect the surface from corrosion (FIG. 7c and Table 2). This observation can be supported by a previous study where they found that the incorporation of graphene flake in epoxy coating increased the water contact angle which signifies the hydrophobic properties of graphene that further contributed to the reduction in water uptake amount (T. Monetta et al., Int. J. Corros. 2017, 2017, 1-9). The rating number of 0.05 wt% graphene was 7 (Table 2), which met the ASTM D1654 requirement (rating number > 4). Table 2. Mean creepage and rating number of the samples. | 0.05 wt% graphene | _ 1 .4 _ | _ 7 _ |

Example 5. Pull-off adhesion test

Pull-off adhesion test

Pull-off adhesion test was performed according to ASTM D4541 to evaluate the adhesion strength between paint coating and the substrate. The image of the dolly test equipment and set up is shown in FIG. 8a. Aluminium dollies with a diameter of 20 mm were glued on the surface of the paint (FIG. 8b) and left to cure at room temperature for 24 h. The pull-off test was carried out in triplicate, at a pulling rate of 1 MPa/s, using the Positest AT-A, Defelsko.

Results and discussion

The pull-off adhesion of the paint refers to the bonding between the paint layer and the metal substrate. The higher adhesion strength of the paint will contribute to better barrier properties of the coating system. FIG. 9a shows the adhesion strength of the epoxy paint coatings as a function of graphene concentration. The adhesion strength of 0.05 wt% graphene was approximately 2400 psi. Compared to the neat paint coating, adhesion strength was observed to increase significantly, by some 50%, with the addition of 0.05 wt% graphene. However, the results of the 0.01 wt% graphene modified paint coating did not reveal any appreciable improvement in adhesion performance. The improvement in adhesion strength is hypothesized to be due to the reduction of porosity in the paint layer by the graphene incorporation, which leads to better surface interaction between the paint and the coated substrate (D. H. Abdeen et al., Materials 2019, 12, 210). It is noted that poor adhesion would accelerate the degradation of the paint as the aggressive ion will start accumulating between the coating and metal interface (T. Monetta et al., Int. J. Corros. 2017, 2017, 1-9). As shown in FIG. 9b, the adhesion performance for both the coating systems was also investigated after 2 weeks of salt spray exposure. The study revealed that both coatings demonstrated some reduction in the adhesion strength after exposure. However, the adhesion strength of the modified graphene paint remained higher than that of the unmodified one even after salt spray exposure. This finding elucidates that the incorporation of graphene could improve the durability of the coating properties even for long-term exposures.

Example 6. Impact test

Impact test

The impact test was carried out according to ASTM D2794. FIG. 10 depicts the experimental setup. Results and discussion

No surface cracking was observed in the samples (FIG. 11). Therefore, the samples passed the pin hole detection test.

Example 7. Cyclic UV/salt spray test

Cyclic UV/salt spray test

To simulate the actual exposure conditions under sunlight and rain or dew, the test samples were exposed to 72 h of salt spray, 16 h of air drying, and 80 h of UV exposure alternately until the cycle was completed for 4200 h. The test procedure was established in accordance with the ASTM D5894. The UV chamber was set at 60 °C for 4 h while the UV condensation was set at 50 °C for 4 h under UV A-340 lamp. As for the salt spray, the test was set at ambient temperature for 1 h of fog cycle and at 35 °C for 1 h of drying. FIG. 12 depicts the experimental setup.

Results and discussion

The cyclic UV and salt spray test was carried out to assess the stability of the paint under extreme condition and to simulate the actual service condition of the coating offshore. As described above, the painted plate for graphene-modified epoxy GF paint and unmodified paint were exposed for one week under UV at 60 °C and one week under salt spray chamber at 35 °C, alternately. The cycle was continued until it completed 25 cycles or 4200 h of exposure. The appearance of the graphene-modified epoxy GF paint surface before and after cyclic UV/salt spray exposure is shown in FIG. 13. It can be clearly seen that both systems experienced some fading of colour after 4200 h of exposure (shown in the rectangle). The unmodified epoxy GF paint was 0.1 % rusted and had a rust grade of 8 but no blistering was observed. However, for graphene modified epoxy GF paint, no rusting or blistering was observed on the surface of the paint, suggesting that the graphene particles are excellent for shielding the paint layer from water ingress and UV attack. The rust grade for 0.05 wt% graphene was 10. Both the system with and without graphene met the ASTM D1654 requirement. However, the rating for 0.05 wt% graphene was better than unmodified paint system.

As previously reported (N. Nuraje etal., ISRN Polymer Sci. 2013, 2013, 1-8; and H. Alhumade et al., Express Polym. Lett. 2016, 10, 1034-1046), graphene is able to absorb most of the incident light and provide hydrophobicity properties to the coating materials. However, in the case of unmodified epoxy paint, a small rusting dot was observed on the surface of the paint (pointed with an arrow) which indicates the deterioration of the paint. This study further confirmed that the introduction of 2D materials, such as graphene, into the coating could act as a reinforcement that binds the coating and metal substrate, and increases the resistance of the coating from external factors such as UV degradation and corrosion. In fact, long term environmental study of the graphene paint under cyclic UV and salt spray exposure demonstrated 2 times improvement in corrosion resistance and satisfied PTS standard requirement for “protective coating and lining” (PTS 152003-2019).

Based on the accelerated long-term salt spray and UV studies, the modified graphene paint system exhibited an enhanced corrosion resistance with less corrosion and blistering underneath. The incorporation of graphene with the paint also demonstrated superior performance in adhesion strength for both tested specimens before and after 2 weeks of salt spray exposure. This trend proves that the presence of graphene in the epoxy paint is beneficial for enhancing corrosion resistance and minimising paint degradation due to water permeability. The schematic diagram of the function of graphene as a barrier additive is shown in FIG. 14.

Example 8. Cathodic disbondment test

Cathodic disbondment test

The cathodic disbondment test was carried out according to ASTM G8. An intentional holiday of 6 mm diameter was introduced at the centre of the coated plate specimens, and then exposed to 3.5 wt% of NaCI solution for 30 days. The potential between the test specimen and reference electrode was maintained at approximately -1 .5 V. The area of disbonded coating from the intentional holiday was measured at the end of the test period of 30 days.

Results and discussion

Cathodic disbondment is a test used to assess the resistance of cathodic disbonding between the coating and metal substrate, and has a requirement of < 10 mm disbondment. Lower disbondment of the coating area would indicate the coating's ability to prevent corrosion attacks. The disbondment radius for unmodified epoxy paint and graphene-modified epoxy paint was 5.2 mm and 5.6 mm, respectively. Thus, graphene-modified epoxy paint met the requirement of the cathodic disbondment test. As observed in FIG. 15a, the disbondment radius for both unmodified and graphene-modified epoxy paint after 30 days of exposure in 3.5 wt% NaCI was almost similar as there was insignificant difference in their disbondment area. Thus, for future work, the hours of exposure can be extended further to 60 or 90 days to fully understand the function of graphene in enhancing the bonding between paint and substrate.

Comparative Example 1

Graphene paint formulations were prepared from commercial epoxy GF paint + curing agent as a part B, and taken for EIS studies by following the protocol in Example 2 except the EIS was obtained after 2 weeks of exposure in 5% NaCI electrolyte solution. Further, the EIS performance of epoxy GF paint was compared to 0.05 wt% loading of graphene in epoxy GF paint formulation by following the protocol in Example 2 except an exposure time of 164 h was set.

Results and discussion

FIG. 16 shows the EIS results of the graphene paint formulations with commercial epoxy GF paint. FIG. 17 shows the comparison of the EIS performance.